Functional Porous Ionic Polymers as Efficient Heterogeneous Catalysts for the Chemical Fixation of CO2 under Mild Conditions

Abstract

The development of efficient and metal-free heterogeneous catalysts for the chemical fixation of CO2 into value-added products is still a challenge. Herein, we reported two kinds of polar group (−COOH, −OH)-functionalized porous ionic polymers (PIPs) that were constructed from the corresponding phosphonium salt monomers (v-PBC and v-PBH) using a solvothermal radical polymerization method. The resulting PIPs (POP-PBC and POP-PBH) can be used as efficient bifunctional heterogeneous catalysts in the cycloaddition reaction of CO2 with epoxides under relatively low temperature, ambient pressure, and metal-free conditions without any additives. It was found that the catalytic activities of the POP-PBC and POP-PBH were comparable with the homogeneous catalysts of Me-PBC and PBH and were higher than that of the POP-PPh3-COOH that was synthesized through a post-modification method, indicating the importance of the high concentration catalytic active sites in the heterogeneous catalysts. Reaction under low CO2 concentration conditions showed that the activity of the POP-PBC (with a conversion of 53.8% and a selectivity of 99.0%) was higher than that of the POP-PBH (with a conversion of 32.3% and a selectivity of 99.0%), verifying the promoting effect of the polar group (−COOH group) in the porous framework. The POP-PBC can also be recycled at least five times without a significant loss of catalytic activity, indicating the high stability and robustness of the PIPs-based heterogeneous catalysts.

Design and Construction of an Azo-Functionalized POP for Reversibly Stimuli-Responsive CO2 Adsorption

“…Notably, after 5 h of UV irradiation, JJU-2 exhibits different CO 2 sorption behaviors due to the trans/cis isomerization of azobenzene in its porous structure. As shown in Figure 4 b, the CO 2 sorption amount decreases to 62 cm 3 g −1 at 273 K and 34 cm 3 g −1 at 298 K. Similar to the previous reports [ 58 , 59 , 60 ], the hysteresis of the CO 2 desorption is mainly ascribed to the electronic attraction between adsorbed and desorbed CO 2 molecules, and the interaction between the porous skeleton and CO 2 . Meanwhile, it is probably caused by the pore window and pore expansion in POPs.…”

Construction of silsesquioxane and phosphinum‐based ionic porous hypercrosslinked polymers for efficient heterogeneous catalytic CO2 cycloaddition

“…The targeted ionic porous hypercrosslinked polymers P-iPHCP-x (x = 21, 11, 12 and 14) were synthesized in high yields over 86% by varying the molar ratios of VPOSS to [PPh 3 Me]Br through the AlCl 3 -catalyzed Friedel-Crafts reaction, while the active mixed anions Cl À , Br À and [AlCl 3 Br] À via ion-exchange and coordination interactions. It is worth noting that the commercially available organic ionic salt [PPh 3 Me]Br has a low price of $33 USD/kg, which is much lower than those of many well-designed vinyl-functionalized phosphinum-based ionic monomers 25,26,30 and other phenyl-contained organic salts (e.g., imidazolium salts). 33,[46][47][48] After the Friedel-Crafts reaction between crystalline monomers VPOSS and [PPh 3 Me] Br in one-pot, the obtained typical polymer P-iPHCP-14 lost most of the characteristic sharp Bragg diffraction peaks that can be assigned to raw crystalline monomers, indicating the formation of a non-crystalline polymer.…”

“…Noticeably, a series of metal-free or metal-coordinated phosphonium-based iPOPs were prepared by initiatorinvolved free-radical polymerizations of speciallydesigned vinyl-functionalized phosphinum-based ionic monomers with diverse substituent groups. [25][26][27][28][29][30] Besides, some phosphonium-based iPOPs were also synthesized by post-ionization of tris(4-vinylphenyl) phosphine-derived neutral POPs. 31,32 Indeed, the above phosphinum-based iPOPs largely depend on the use of functional phosphinum-based ionic monomers with halogen and vinyl groups, however, these high-cost phosphinum salts are not commercially available and required to be pre-prepared by complex and multi-step synthetic processes.…”

“…25 It was noted that the introduction of electrophilic sites including metal complexes and hydrogen bond donors (HBDs, for example, hydroxyl and carboxyl groups) into iPOPs could promote the catalytic efficiency by the synergistic catalysis of nucleophiles and electrophiles for the activation and conversion of CO 2 and epoxides . [26][27][28][29][30][31] To the best of our knowledge, it was seldomly reported that iPOPs catalysts could simultaneously combine with multiple active sites related to nucleophilic halogen anions, electrophilic Lewis acidic metal sites and HBD groups. 33 Based on the focused two aspects both in synthesis and catalysis, it is strongly desirable to construct phosphinum-based iPOPs with multiple active sites using low-cost phosphinum ionic salts in a one-pot strategy, which can be used as highly efficient allin-one heterogeneous catalysts for CO 2 cycloaddition under mild conditions.…”

A stable nanotubular metal–organic framework as heterogeneous catalyst for efficient chemical fixation of CO2

“…However, they often are operated under harsh reaction conditions (initial CO 2 pressure >1.0 MPa and/or reaction temperatures >80 °C). There are many reports of this reaction under mild conditions, 12 such as the polar-group-functionalized porous ionic polymer (PIP) POP-PBH, 13 which could promote the cycloaddition reaction of CO 2 with epichlorohydrin as an efficient bifunctional heterogeneous catalyst with 1.0 mol% catalyst loading at a relatively low temperature (60 °C) and ambient pressure under metal-free conditions during a reaction time of 48 h. Therefore, increasing efforts are being devoted to developing efficient catalysts for the solventless synthesis of cyclic carbonates to take place under milder reaction conditions, including lower initial CO 2 pressure, lower catalyst loading and shorter reaction time.…”